Network system and method for automatically interfacing with communication apparatus of different standard

ABSTRACT

A communication apparatus including a network control unit for interfacing with a telephone line. The network control unit comprises a direct current circuit in which a loop state direct current can flow, and a direct current limiting device for limiting the loop state direct current to a prescribed value when communication with a foreign country that has adopted a different communication standard is performed.

CROSS-REFERRENCE TO RELATED APPLICATIONS

[0001] This application claims priority of Japanese Patent ApplicationNos. 11-278611 filed on Sep. 30, 1999 and 2000-066984 filed on Mar. 10,2000, the entire contents of which are hereby incorporated herein byreference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to a communicationapparatus, and in particular relates to a telephone line interfacebetween a facsimile and a copier, a printer, and/or a card MODEM or thelike that has a facsimile function.

[0004] 2. Discussion of the Background Art

[0005] Recently, communication standards adopted by European countrieshave been unified into the Common Technical Regulation 21 (hereinafterreferred to as the CTR 21).

[0006] However, the characteristics of a direct current that flowsthrough a network control section of a communication apparatus, e.g., afacsimile, are different from those of the conventional standard.Namely, a direct current is required to have nonlinear characteristicsthat arise due to limits on a direct current that flows through a directcurrent circuit.

[0007] Further, since communication standards adopted by many countries(excepting Europe) are not uniform, linear characteristics are requiredin several countries, and the direct current characteristics must bechanged to those of a destination country.

[0008] Therefore, two different baseboards for generating directcurrents with different characteristics are necessary in the networkcontrol section of communication apparatus when communication withanother country that has adopted a different communication standard isperformed. Namely, a network control unit having both a backgrounddirect current circuit which does not limit a direct current to aprescribed value and that having the direct current circuit for the CTR21 use, i.e., which limits a direct current, should be provided.

[0009] Further, the characteristics of a network, except for externalline network connections executed by a public exchanger based on thePost Telephone Telegram standard (hereinafter referred to as the PTTstandard) of the country, are sometimes not based on the PTT standard ofthe applicable country.

[0010] Specifically, an internal line exchanger that operates with aconstant current is included among internal line exchangers, such as asmall business use internal exchangers (hereinafter referred to as aPABX), a home PABX, and large scale exchangers employed in a business asa private line.

[0011] When using such an internal line exchanger, it has been shownthat it is impossible to form a network connection between acommunication apparatus and an internal line exchanger if thecommunication apparatus operates at a current value in excess of theprescribed limit upon the direct current. This is because the networkcharacteristic of the internal line exchanger generally depends upon themanufacturer.

[0012] Further, there are strict standards for parameters related tocontrol operations of the general public line networks above and beyondother networks. However, parameters related to control operations ofother networks can be, to a large degree, set in consideration ofgeneral-purpose uses. Thus, the above-mentioned current limitation isgenerally not applied in internal line exchangers.

[0013] For example, the Japanese Patent Application laid Open No.8-335994 describes technology related to the above-mentioned apparatus.The technology changes the characteristics of the direct current basedon a country by connecting resistors in parallel to a photo relay.Thereby, it is possible to generate a direct current in accordance witha standard of the telephone line of an applicable destination countryusing a direct current generating circuit with a simple construction.

[0014] However, the above-mentioned related technology can not generatea direct current that includes nonlinear characteristics that limit acurrent flowing through the circuit to a prescribed value. Further, itis not necessary (or, in some cases, desirable) to directly limit acurrent that flows through a circuit when controlling a network exceptwhen the network is the general public line network. This is thus asource of problems.

SUMMARY OF THE INVENTION

[0015] The present invention has been made in view of the above notedand another problems and one object of the present invention is toaddress and resolve such problems.

[0016] A further object of the present invention is to provide a novelcommunication apparatus including a network control unit configured tointerface with a telephone line. The network control unit may include adirect current circuit configured to carry a loop state direct current,and an electrical characteristic changing device configured to changeone or more electrical characteristics of the direct current circuit sothat the one or more electrical characteristics of the direct currentcircuit complies with a communication standard adopted by the othercommunication apparatus.

[0017] In yet another embodiment, the one or more electricalcharacteristics may include a limit (to a prescribed value) on a loopstate direct current flowing through the direct current circuit, as wellas a lack of limits thereon.

[0018] In yet another embodiment, the one or more electricalcharacteristics may be a limit upon the direct current whencommunication with a prescribed foreign country occurs.

[0019] In yet another embodiment, the one or more electricalcharacteristics may be changed based on a designation of the foreigncountry.

[0020] In yet another embodiment, an electrical characteristicalternating device may be provided to selectively alternate one of aplurality of electrical characteristic with another in correspondencewith a kind of communication used and/or desired.

[0021] In yet another embodiment, the kind of communication may includeexternal line communication and internal line communication.

[0022] In yet another embodiment, the one or more electricalcharacteristics may be alternated with those of a direct currentlimiting mode when the communication is transmitted to and from anexternal line.

[0023] In yet another embodiment, a current limiting device may beprovided in the direct current circuit to limit a direct current flowingthrough the direct current circuit to a prescribed value.

[0024] In yet another embodiment, a switching device may be provided toselect either a direct current limiting circuit configured to limit adirect current to the prescribed value or a direct current non-limitingcircuit configured not to limit the direct current.

[0025] In yet another embodiment, a display device may be provided todisplay a screen through which either a direct current limitation mode,where a loop state direct current is limited, or a direct currentnon-limitation mode, where a loop state direct current is not limited,is set and/or selected.

[0026] In yet another embodiment, a dial call-generating device may beprovided for generating a dial pulse or a tone signal, and the directcurrent limit is removed when the dial pulse or the tone signal relatesto a network other than the general public line.

[0027] In yet another embodiment, the direct current limit may beimplemented only when a dialed number of the dial call-generating deviceincludes a prescribed number representing external communication.

[0028] In yet another embodiment, a ringing signal detection device maybe provided for detecting a ringing signal, and the switching device maybe controlled to switch to a direct current non-limiting mode when aringing wave detected by the ringing signal detection device indicatesreception from a network other than the general public line.

[0029] In yet another embodiment, a parameter generating device may beprovided to generate a parameter representing a limit on the directcurrent, and the parameter need not be generated and included inparameters related to the control of the network when communication ispracticed via a network other than a general public line.

[0030] In yet another embodiment, the parameter is set using the settingswitch or a screen provided in the communication apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] A more complete appreciation of the present invention and many ofthe attendant advantages thereof will be readily obtained as the samebecome better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

[0032]FIG. 1 is a chart illustrating an exemplary construction of thefacsimile apparatus of the first embodiment according to the presentinvention;

[0033]FIG. 2 is a chart illustrating an exemplary construction of thenetwork control section of the facsimile apparatus illustrated in FIG.1;

[0034]FIG. 3 is a chart illustrating an exemplary construction of thedirect current circuit of the network control section illustrated inFIG. 2;

[0035]FIGS. 4A and 4B are graphs illustrating exemplary electricalcharacteristics of the direct current circuit, i.e., the direct currentcircuit having non-linear characteristics and the direct current circuithaving linear characteristics;

[0036]FIG. 5 is a chart illustrating an exemplary construction of thedirect current circuit of the second embodiment;

[0037]FIG. 6 is a flowchart illustrating an exemplary switchingoperation for switching to a direct current limiting mode, executed at atime of call generation in the second embodiment;

[0038]FIG. 7 is a flowchart illustrating an exemplary switchingoperation for switching to a direct current limiting mode, executed at atime of reception in the second embodiment;

[0039]FIG. 8 is a flowchart illustrating an exemplary switchingoperation for switching to a direct current limiting mode, executed inthe third embodiment;

[0040]FIG. 9 is a flowchart illustrating an exemplary switchingoperation for switching to a direct current limiting mode, executed at atime of call generation in the fourth embodiment; and

[0041]FIG. 10 is a flowchart illustrating an exemplary switchingoperation for switching to a direct current limiting mode executed at atime of reception in the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0042] Referring now to the drawings, like reference numerals and marksdesignate identical or corresponding parts throughout several views.

[0043] The first embodiment is now described referring to FIGS. 1, 2 and3. A principal control section 21 may include a central processing unit(hereinafter referred to as a CPU) or similar device and performprocessing operations of internal sections and its elements of thefacsimile apparatus according to a variety of control programs stored ina ROM 23.

[0044] A RAM 24 may store a variety of data and include a work area foruse in the control of the facsimile apparatus. The RAM 24 may store apredetermined dial number, such as zero, used when switching from aninternal line to an external line, a predetermined dial number used whenswitching to an internal line from an external line, a frequency of aringing wave of an internal and/or external line, and/or a cadenceON/OFF time period representing signal ON/OFF timing or the like.Furthermore, the RAM 24 may double as an image memory for storing imagedata encoded by an encoding/decoding section 25. The encoding/decodingsection 25 may compress transmission image data using a prescribedencoding method, such as the MH•MR•MMR encoding method, and may expandand decode reception image data using a prescribed decoding method, suchas the MH•MR•MMR decoding method.

[0045] A recording section 26 may be provided and may be composed of aconventional electrophotographic system that performs processes such ascharging., tracing, exposing, developing, discharging, transferring,separating, and cleaning operations or the like. The recording section26 may print out image data read, image data received, and a report orthe like with a prescribed resolution. The image data received may beprinted out on a transfer sheet with a prescribed line density, e.g.,3.85 lines, 7.7 lines, or 15.4 lines per millimeter. A reading section27 may be provided to optically read, line by line, an original image ata prescribed resolution, and may convert the original image into imagedata at a corresponding line density.

[0046] An operating section 28 may be provided and include the followingkeys. It may include a start/stop key for generating a trigger signalfor each operation, a ten key group as a dial keypad, a one-touch key, asetting/resetting key for setting and resetting a variety of modes, acountry designating key for designating a facsimile by country, and/or afunction key for performing a variety of other processes. The operatingsection 28 may transmit information to the principal control section 21when any of keys is pressed.

[0047] A display section 29 may be provided and include a displaydevice, such as a liquid crystal display and/or a light emitting diode.The display section 29 may display information and after it has beeninputted and set by the operating section 28 so that a user can confirmthe contents thereof.

[0048] A MODEM 22 may be connected to a line 3 via a network controlsection 1. The MODEM 22 may modulate image data to be transmitted to theline 3, and may decode a signal received from the line 3 via the networkcontrol section 1. Further, the MODEM 22 may transmit a DTMF or PBsignal, detect a reception signal, and switch from a telephone mode to afacsimile mode, and/or vice versa, thereby performing the prescribedfacsimile transmission control operations.

[0049] A network control section 1 may be provided and include aringing/OFF-hook detection device having a later-described call signaldetection circuit 19, a dial call generation device including alater-described photo-coupler 14 and a transducer 17, and alater-described direct current circuit 15 or the like.

[0050] A network control section 1 may perform a prescribed line controloperation during both signal transmission and reception using theprincipal control section 21 and control the cut off operations andestablishment operations of the line. Furthermore, a handset, not shown,may be connected to the network control section 1 and utilized fortelephone communication or the like with the other office.

[0051] Further, a power source voltage may be supplied to each unit ofthe facsimile when the principal control section 21 transmits a powersource control signal to a power source switching section (not shown).Furthermore, each section may perform any necessary data communicationvia a bus line. The network control section 1 may include the followingdevices illustrated in FIG. 2. A relay 12 capable of connecting to theline 3 through a connection that corresponds to a telephone mode(hereinafter referred to as a “TEL” mode) or a facsimile mode, a currentsensor 11 that detects a current flowing through the line 3, and a CNGtone detecting circuit 19 for detecting a tone signal, such as CNG, thatindicates that a communication transmitter is a facsimile apparatus, maybe provided. A call signal detecting circuit 18 for detecting a ringingsignal and binalizing its ringing wave, and a diode bridge 13 foradjusting a polarity of the direct current voltage may be provided.

[0052] Further, a direct current circuit 15 in which a loop state directcurrent can flow, a photo-coupler 14 for controlling opening/closingoperations of the direct current loop, i.e., controlling direct currentON/OFF operations, and allowing transmission of a dial pulse of arecipient identification number may also be included. A condenser 16that does not pass a direct current, and a transducer 17 fortransmitting a signal from a primary side to a secondary side andtransmitting a DTM or PB signal from the MODEM 22 may be also provided.A prescribed circuit for switching from a two-line side (a line side) toa four-line side (a MODEM side), or vice versa, may be connected to thesecondary side (winding) of the transducer 17.

[0053] The direct current circuit 15 is now described in more detailreferring to FIG. 3. The direct current circuit 15 may include fourresistors R1 through R4, and two transistors Tr1 and Tr2. Among those,the transistors Tr2 or similar devices arranged in the route B may forma direct current limiting circuit.

[0054] A communication operation of the facsimile apparatus is nowdescribed. Before a ringing signal is detected and facsimilecommunication is performed, the relay 12 illustrated in FIG. 2 isswitched to the side of the call signal detecting circuit 18, i.e., theTEL (hand set) side.

[0055] A call signal from the line is detected by the call signaldetecting circuit 18, and a detection signal is generated.

[0056] The detection signal is then inputted to the CPU of principalcontrol section 21, and it is determined if the detection signalindicates a prescribed call signal corresponding to a facsimilecommunication. If the detection signal is a prescribed call signal, therelay 12 is switched to the transducer side 17 with a commandtransmitted from the CPU, and thereby the line 3 is closed.

[0057] Then, a direct current flows into the direct current circuit 15via the photo coupler 14 from a positive side of the diode-bridge 13.Thereby, a direct current loop is formed.

[0058] The direct current then enters the negative side of the diodebridge 13, and is outputted to the line 3 via the relay 12.

[0059] A plurality of signals from the facsimile communication may enterinto the diode bridge 13 from the line via the relay 12, and they may beoutput from the positive side of the diode bridge 13. Then, the outputenters the transducer 16 via the photo coupler 14, the direct currentcircuit 15, and the condenser 16. A signal appearing at one end of theprimary side winding when a current flows through the primary sidewinding may enter the negative side of the diode bridge 13 via thedirect current circuit 15, and return to the line via the relay 12.

[0060] Further, the signals transmitted to the secondary side of thetransducer 17 are separated into a transmission signal and a receptionsignal using a conventional two-line circuit and four-line circuit (notshown). After that, the signals may be transmitted to the MODEM, and aremodulated and demodulated as appropriate.

[0061] A transistor Tr2 (and similar devices) provided in the route Billustrated in FIG. 3 might form a direct current limiting device. Arelay and a photo-coupler or similar devices may constitute a switchingdevice 151 illustrated in FIG. 5. The operating section 28 and theprincipal control section 21 or the like may constitute a designationdevice. The network control section 1 including the photo-coupler 14 andthe transducer 17 or the like may constitute a dial call-generationdevice. The display section 29 or the like may form a display device.The operating section 28 or the like may form a setting device. Further,the network control section 1 including the call signal detectioncircuit 19 may constitute a ringing (signal) detection device.

[0062] A direct current limiting operation of the direct current circuit15 is now described in detail referring to FIGS. 3 and 4. When a linevoltage is applied to the direct current circuit 15 and is voltagedivided by the resistors R2 and R3, some current may flow (or asufficient voltage may be applied, as appropriate) to the base of thetransistor Tr1. As a result, the base reaches a prescribed, transistoractivating, voltage level, and some current flows from the collector tothe emitter of the transistor Tr1, and accordingly, through the route A.

[0063] When the current is relatively small, the line voltage mayincrease in proportion to the product of the sum of the resistances ofresistors R1 and R5 with a magnitude of the current, because the currentflows almost exclusively through the resistors R1 and R5 of the route A.When the line voltage is additionally supplied by certain types ofexchangers (not shown), a current that is larger than a prescribed valuemay flow through the resistor R1. This is because the magnitude of thecurrent flowing through the circuit may increase as a result of theapplication of the additional voltage.

[0064] Furthermore, a current may flow (or a voltage may be applied to,as appropriate) to the base of the transistor Tr2 through the resistorR4, and thereby the base may reach a prescribed voltage value activatingthe transistor Tr2. With the transistor Tr2 in the active state, a smallmagnitude current may flow from the emitter to the collector of thetransistor Tr2, and further flow through the resistor R2. Then, sincethe resistance of the resistor R2 is large enough, the voltage of theline 3 may increase, even if the current is small. Thus, the currentflowing through the direct current circuit 15 is limited to a prescribedvalue. Namely, a large line voltage may be required when more currentflows through the route A due to an increase in the voltage across theresistor 2.

[0065] Accordingly, the direct current having nonlinear characteristics(i.e., the current is substantially limited to a prescribed magnitude)as illustrated in FIG. 4B, can be attained. Since it is required by theEuropean unified standard (CRT 21) to limit the current to 40 mA, avalue of the resistor R1 may be chosen while considering of theactivation voltage of the transistor Tr2.

[0066] Since the flow of current may be determined by the resistance ofthe resistor R4, nonlinear direct current characteristics such as thoseillustrated in FIG. 4B can be attained by adjusting the resistor valuein correspondence with the requirements of CRT 21.

[0067] As mentioned earlier, the nonlinear direct currentcharacteristics are inherent to the European unified standard, whereasthe direct current characteristics in countries that do not employ theunified European standard are generally linear. Further, the directcurrent characteristic for internal line exchangers, such as a PABX, isgenerally linear.

[0068] The second embodiment is now described referring to FIG. 5. Anembodiment of another the direct current circuit 15 is illustratedtherein. The construction of a network control section 3 and a facsimileapparatus are substantially the same as in the first embodiment.

[0069] A switching device 151 may be provided between a transistor Tr2and the resistor R2 in the direct current circuit 15, and may beconfigured to optionally connect to and disconnect from a route B. Theswitching device 151 may be formed from a relay or a photo coupler or asimilar device controlled by the principal control section 21 via asignal line (not shown).

[0070] A setting operation for setting an operating condition of therelay, i.e., either limiting a direct current or not, can be performedin the following manner. A service person or a user may operate adisplay section 29 using a key or a similar device provided on theoperating section 28, and may display a selection screen.

[0071] The service person may then select and input to the selectionscreen ON/OFF signals, respectively representing that the direct currentlimiting operation should be one of executed and stopped. The inputtedcontents may be transmitted from the operating section 28 to theprincipal control section 21, and may be set and stored in a directcurrent limitation ON/OFF flag provided in the RAM 24. The principalcontrol section 21 may instruct the switching device 151 to set andclear direct current limitation and non-limitation modes via the signalline, and may control direct a current to flow through either of theroutes A or B.

[0072] When the route B is cut off between the transistor Tr2 and theresistor R2, a current may flow only through the route A, and directcurrent characteristic satisfying the linear type standard asillustrated in FIG. 4A may be obtained. A direct current limitingoperation executed when any call such as a telephone call or a facsimilecall is generated is now described referring to FIG. 6. The dial callgeneration should be an auto call generation.

[0073] When a call is to be generated, i.e., a user starts inputting adial number as a transmission sign through the operating section 28 (Yesin step S201), the, principal control section 21 may confirm a status ofthe direct current limitation ON/OFF flag corresponding to the dialnumber (in step S202).

[0074] If it determines that the direct current limitation ON/OFF flagis in the active state (Yes in step S202), the principal control section21 may turn ON the relay of the switching device 151 (in step S203).Then, the transistor Tr2 and the resistor R2 are connected to eachother, and thereby it is possible for current to flow through the routeB. Further, by turning ON the photo coupler 14 and thereby closing adirect current loop (in step S204), a direct current is simultaneouslylimited to a prescribed value. As a result, a direct current havingnonlinear characteristics may be generated, because the route B maylimit a current flowing through the direct current circuit in a samemanner as mentioned earlier.

[0075] Hence, the photo coupler 14 may be turned ON/OFF when dial pulsesare to be transmitted. The MODEM 22 may execute dial call generation (instep S205) when a DTMF as a tone signal or a PB signal as a dial pulsesignal is transmitted. After that, when communication and dialog arecompleted (in step S206), the direct current loop may be opened as asign of completion of the communication and dialog (in step S207), andthe relay of the switching device 151 may be turned OFF (in step S208).Thereby, all operations are finalized.

[0076] On the other hand, if it is determined in step S202 that thedirect current limitation ON/OFF flag is in the OFF state, the relay ofthe switching device 151 may not be turned ON, i.e., it retains aninitial state or an OFF state, and thereby the route B is cut offbetween the transistor Tr2 and the resistor R2. The direct current loopmay then be closed by turning ON the photo coupler 14 (in step S209),and direct current having linear characteristics may be generated by theroute A. Further, a prescribed call generating operation may be executedas mentioned above (in step S210). When communication and dialog arecompleted (in step S211), the direct current loop is opened, and therebyall operations are finished (in step S212).

[0077] A direct current limiting operation that is performed during anyreception is now described referring to FIG. 7. Ringing reception shouldbe auto reception.

[0078] When a ringing signal (as a sign of reception) is input from theline 3 via a call signal detection circuit 18 (Yes in step S301), theprincipal control section 21 may confirm the direct current limitationON/OFF flag stored in the RAM 24 corresponds to the ringing signal.

[0079] When it is determined that the direct current limitation ON/OFFflag is in the active state, the relay as a switching device 151 isturned ON (in step S303) and the transistor Tr2 is connected with theresistor R2 so that a current flows through the route B. The directcurrent may be limited to a prescribed value in the same manner (asdescribed earlier) when the photo-coupler 14 is turned ON and therebythe direct current loop is closed (in step S304). Thus, a direct currenthaving nonlinear characteristics may be generated by the route B.

[0080] After that, when communication and dialogue are completed (instep S305), the direct current loop is opened (in step S30.6), and theswitching device 151 is turned OFF (in step S307). Thereby, alloperations are finalized.

[0081] On the other hand, when it is determined that the direct currentlimitation ON/OFF flag is not in the active state (in step S302), theswitching device 0.151 is not turned ON, i.e., it keeps an initial stateor an OFF state. After that, the photo-coupler 14 is turned ON, so thatthe direct current loop is closed (in step S308). Thus, the route A, asdescribed earlier, may generate the direct current having linearcharacteristics. When the communication and dialogue are completed (instep S309), the direct current loop is opened (in step S310), and alloperations are finalized.

[0082] Thus, according to this embodiment, a direct current havingnonlinear characteristics may be generated by connecting the transistorTr2 with the resistor R2 having a relatively large resistance via theswitching device 151. Thereby, a current flowing through the directcurrent circuit 15 may be limited to a prescribed value. Further, adirect current having linear characteristic may be generated by breakingthe connection between the transistor Tr2 and the resistor R2 using theswitching device 151. Since a direct current generating mode can beswitched from a current limiting mode to a non-current limiting mode (orvice versa) using substantially the same network control section 1 andthe switching device 151, the facsimile can be used in both types ofcountries, i.e., a country that has adopted the European unifiedstandard and a country that has adopted a different communicationstandard. In addition, a plurality of network control sections 1 is notrequired.

[0083] As a modification, a service person can optionally set a directcurrent limitation ON/OFF mode by switching a bit switch or a dipswitch.

[0084] The third embodiment is now described referring to FIG. 8. Theconstruction of a network control section 1 having a direct currentcircuit is substantially the same as the second embodiment.

[0085] A switching condition of the switching device 151 may bepredetermined depending on a country, so that electrical characteristicsof the direct current is recorded for each country beforehand. Namely,information related to the country including a name, a country code,code number, or the like may be stored in a RAM and/or similar devices.Further, the principal control section 21 may switch the switchingdevice 151 based on the information, i.e., the switching condition.

[0086] Specifically, a prescribed country is designated (in step S101)by operating a country designation key provided on the operating section28 when a facsimile apparatus is to be purchased or shipped. The countrydesignation information is transmitted from the operating section 28 tothe principal control section 21, and the country is recognized. It islater determined if the standard of the country is linear (in stepS102).

[0087] If the standard is linear, the transistor Tr2 and the resistor R2are disconnected from each other and accordingly, the route B is cutoff. Thus, a direct current having linear characteristics may begenerated by the route A (in step S104). On the other hand, when thestandard of the country is nonlinear, the transistor Tr2 and theresistor R2 may be connected with each other and a direct current mayaccordingly be limited by the route B. Thereby, a direct current havingnonlinear characteristics may be generated (in step S105).

[0088] According to the third embodiment, since the switching device 151may automatically operate according to a communication standard of thecountry to which the communication is transmitted or from which thecommunication is received, when a prescribed country is designated, thedirect current characteristics can properly and automatically beattained using a facile operation.

[0089] The fourth embodiment is now described referring to FIGS. 9 and10. A construction of a network control section 1 having a directcurrent circuit 15 is substantially the same as in the secondembodiment. The network control sectional may include a photo-couplerand a transducer or the like. The network control section 1 may includea call signal detection circuit 19 or the like. When call is generated,the principal control section 21 may determine from a dial pulse or adial number of a DTMF signal or a PB signal transmitted from the networkcontrol section 1, whether it is communication to be practiced by thegeneral public line network or the other. An ON/OFF operation may beautomatically executed by the switching device 151 based on thedetermined result. Specifically, since external line call generationoccurs when the dialed number is zero, the switching device 151, only inthis case, may connect the transistor Tr2 to the resistor R2.Accordingly, a direct current having nonlinear characteristics suitablefor the European unified standard is generated, and thus the currentflowing through the circuit is limited to a prescribed value, asmentioned earlier.

[0090] On the other hand, when any call signal is received and detectedby the network control section 1, the principal control section 21 maycompare the ringing wave of the call signal with ringing waveinformation, e.g., network control use parameters for the general publicline, which has been previously stored in the RAM 24 or the ROM 23. Ifthose correspond to one another, since the ringing wave may be assumedto be transmitted from the external line, i.e., communication from thegeneral public line network, a direct current having nonlinearcharacteristics may be generated. This may be done by operating theswitching device 151 in the same manner as mentioned earlier only inthis case.

[0091] To execute the above-mentioned operation, prescribed informationrepresenting transmission from the external line and the otherrepresenting transmission from the internal line, for example, may bepreset through the operating section 28 and stored in the RAM 24, sothat an internal line, i.e., a line except for the general public line,and an external line, i.e., the general public line can be recognized.Further, a variety of parameters, such as the wave of a ringing signaland its level or the like, related to network control and indicative ofeither external or internal lines, can be previously inputted and setusing the bit switch or similar devices provided on the operatingsection 28. These parameters can also be stored in the RAM 24. Suchinformation may be referred to when determining if the transmission isfrom either the internal line or the external line.

[0092] A direct current limiting operation executed in this embodimentwhen any call is generated is now explained referring to FIG. 9. Thisembodiment presupposes that external call generation requires a directcurrent limiting operation, and a switching operation for switching tothe external line is executed when the first dialed number is zero.Further, internal call generation does not require the direct currentlimiting operation, and is performed when the first dialed number is notzero. Further, dial call generation should be auto call generation.

[0093] When a user starts inputting a dial number of a recipient as atransmission signal through the operating section 28 (in step s401), theprincipal control section 21 may compare the dial number with aprescribed internal/external switching number stored in the RAM 24 (instep S402).

[0094] If the leading number is zero (in step S403), since it representsthe external line call generation, the relay of the switching device 151is turned ON (in step S404), and the transistor Tr2 is connected to theresistor R2, thereby enabling a current to flow through the route B.Further, the direct current loop is closed by turning ON thephoto-coupler 14 in the earlier mentioned manner (in step s405), andthereby the route B limits the current flowing through the directcurrent circuit 15. Thus, a direct current bearing nonlinearcharacteristic may be generated.

[0095] A call generating operation may then be executed (in step S406).The direct current loop may be opened (in step S408) and the relay asthe switching device 151 may also be turned OFF (in step s409) whencommunication and dialogue are completed (in step S409). Thereby, alloperations are finalized.

[0096] On the other hand, since internal call generation occurs when thefirst dialed number is not zero, control section 21 does not turn ON theswitching device 151, i.e., it retains an initial state or an OFF state,and may disconnect the transistor Tr2 from the resistor R2. In otherwords, the route B does not conduct significant amounts of current (instep S403). Further, the principal control section 21 may close thedirect current loop by turning ON the photo-coupler 14 (in step s410).Thereby, a direct current having linear characteristics may be generatedusing the route A in the same manner as mentioned earlier. A callgenerating operation may then be executed (in step s411). The directcurrent loop may be opened (in step S413), when the communication anddialogue are completed (in step S412), thereby finalizing alloperations.

[0097] A direct current limiting operation in this embodiment executedwhen any reception is made is now explained referring to FIG. 10. It maybe determined from, for example, the frequency of the ringing wave, it'scadence, and/or an ON/OFF time period, that the reception of either anexternal line communication requiring direct current limitation or aninternal line communication not requiring the direct current limitationhas occurred. The ringing signal reception should be executed byautomatic recognition of a ringing signal and the reception thereof.

[0098] When a ringing signal is used as a reception sign and is inputfrom the line 3 (in step S501), the principal control section 21 maycompare the ringing signal with the ringing parameters of the internaland external lines stored in the RAM 24. This corresponds to examiningthe ringing wave in step s502. If the received signal is determined tooriginate from the external line (in step S503), since direct currentlimitation is required, the relay switching device 151 is turned ON asdescribed earlier (in step S504), and the transistor Tr2 is connected tothe resistor R2.

[0099] Further, a direct current loop is closed by turning ON thephoto-coupler 14 (in step S505), and a direct current having nonlinearcharacteristics is generated. This occurs because a current flowing thedirect current circuit is limited by the route B in the same manner asmentioned earlier. When communication and dialogue are completed (instep S506), the direct current loop is opened (in step S507) and therelay of the switching device 151 is turned OFF (in step S508). Thereby,all operations are finalized.

[0100] On the other hand, if the received signal is determined tooriginate from the internal line (in step s503), a direct currentlimitation is not required the switching device 151 is not turned ON. Inother words, the switching device 151 retains the initial state or theOFF state. Thus, the transistor Tr2 remains disconnected from theresistor R2. When the photo-coupler 14 is turned ON, and accordingly thedirect current loop is closed (in step S509), a direct current havinglinear characteristics may be generated by the route A with the route Bbeing disconnected. When communication and dialogue are completed (instep S510), the direct current loop is opened (in step S511), and alloperations are finalized.

[0101] As a modification in some embodiments, an internal line button(that is pressed when internal line transmission is performed) and anexternal line button (that is pressed when external line transmission isperformed) can be provided. Thus, an operation similar to the “zero callgeneration” mentioned earlier can be performed when the external linebutton is pressed. In this case, a step for determining if the internalor external line button has been pressed may substitute for the stepsfrom S401 to S403 mentioned above.

[0102] As another modification in some embodiments, if the internal lineuse parameter can be extensively set more easily than the external lineuse parameter, then a parameter representing non-direct currentlimitation can be added to the internal line use parameters. In thiscase, the relay switching device 151 can be turned OFF using theparameter when the mode is switched to the internal line mode. The relayof the switching device 151 may be turned ON when a mode is switched tothe external line mode.

[0103] As yet another modification, a parameter representing directcurrent limitation can be added to the external line use parameters, andthe relay of the switching device 151 may be turned ON using theexternal line use parameter in response to switching to the externalline mode. In such a case, a parameter setting screen can be displayedon the display section 29, and a user or the like can set theabove-mentioned internal or external line use parameters with a keyoperation through the operating section 28. Otherwise, a bit switch forsetting a variety of parameters can be provided on the operating section28, and a service person or the like can select and set a prescribedparameter(s) representing either non-direct current limitation or directcurrent limitation as appropriate.

[0104] Thus, it is possible to limit the loop state direct current byinputting a prescribed signal through either the bit switch or thesetting screen as mentioned earlier, and by turning ON the switchingdevice 151 when external line call generation occurs or an external linetransmission is received before closing the direct current loop.

[0105] Thus, a prescribed network interface suitable for the networkcharacteristics of the exchanger can be automatically selected based onwhether line communications are external or internal, since parameter(s)representing non-direct current limitation may be included in theinternal line use parameters and parameters representing direct currentlimitation may be included in the external line use parameters.

[0106] The present invention can include a wide range of applications ofa network control section (NCU) having an interface function with acommunication line in the communication apparatus obviously, numerousadditional modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the presentinvention may be practiced otherwise than as specifically describedherein.

What is claimed as new and desired to be secured by Letter Patent of theUnited States is:
 1. A communication apparatus including a networkcontrol unit configured to interface with a telephone line, said networkcontrol unit comprising: a direct current circuit configured to carry adirect current; and an electrical characteristic changing deviceconfigured to change an electrical characteristic of the direct currentcircuit so that the electrical characteristic of the direct currentcircuit conforms with a communication standard adopted by anothercommunication apparatus.
 2. The communication apparatus as claimed inclaim 1, wherein said another communication apparatus is located in aforeign country.
 3. The communication apparatus as claimed in claim 1,wherein said electrical characteristic includes: a limit upon the directcurrent flowing through the direct current circuit.
 4. The communicationapparatus as claimed in claim 3, wherein said electrical characteristicis a limit upon the direct current related to an identity of a foreigncountry having said another communication device.
 5. The communicationapparatus as claimed in claim 4, wherein said electrical characteristicis changed based on a designation of the foreign country.
 6. Acommunication apparatus including a network control unit configured tointerface with a telephone line, said network control unit comprising: adirect current circuit configured to carry a loop state direct current,said direct current circuit having a plurality of selectable electricalcharacteristics; and an electrical characteristic alternating deviceconfigured to selectively alternate one of the plurality of electricalcharacteristics with another of the plurality of electricalcharacteristics based on a kind of desired communication.
 7. Thecommunication apparatus as claimed in claim 6, wherein said kind ofdesired communication comprises one of an external line communicationand an internal line communication.
 8. The communication apparatus asclaimed in claim 7, wherein said one of the plurality of electricalcharacteristics being a direct current limit when the kind of desiredcommunication is the external line communication.
 9. The communicationapparatus as claimed in claim 6, wherein said plurality of electricalcharacteristics includes: a direct current limit upon the direct currentflowing through the direct current circuit; and a characteristic of nolimit upon the direct current flowing through the direct currentcircuit.
 10. The communication apparatus as claimed in claim 6, furthercomprising: a current limiting device configured to limit a directcurrent flowing through the direct current circuit to a prescribedvalue, said current limiting device being provided in the direct currentcircuit.
 11. The communication apparatus as claimed in claim 10, furthercomprising a switching device configured to select one of the directcurrent limiting device configured to limit the direct current to theprescribed value and a direct current non-limiting circuit configurednot to limit the direct current.
 12. The communication apparatus asclaimed in claim 11, further including a bit switch configured toindicate to said switching device to select one of the direct currentlimiting device and the direct current non-limiting circuit, whereinsaid switching device selecting based on the indication of the bitswitch.
 13. The communication apparatus as claimed in claim 10, furthercomprising a display device configured to display a screen used to setone of a direct current limitation mode and a direct currentnon-limitation mode.
 14. The communication apparatus as claimed in claim11, further comprising a dial call-generating device configured togenerate one of a dial pulse and a tone signal, wherein said directcurrent non-limiting circuit being selected when said one of said dialpulse and said tone signal being associated with a network other than ageneral public line.
 15. The communication apparatus as claimed in claim14, wherein the direct current limiting device being selected when adial number of the dial call generating device includes a prescribednumber indicating an external communication.
 16. The communicationapparatus as claimed in claim 11, further comprising a ringing signaldetection device configured to detect a ringing signal, wherein saidswitching device selecting said direct current non-limiting circuit whena ringing wave of said ringing signal detected by the ringing signaldetection device indicates a reception from a network other than thegeneral public line.
 17. The communication apparatus as claimed in claim11, further comprising a parameter generating device configured togenerate a parameter representing a limitation upon the direct current,wherein said parameter being related to a general public linecommunication.
 18. The communication apparatus as claimed in claim 17,further comprising a setting switch used to set the parameter.
 19. Thecommunication apparatus as claimed in claim 17, further comprising adisplay device configured to display a screen used to set saidparameter.
 20. A method of communicating by interfacing with a telephoneline, comprising the steps of: providing a network control unitconfigured to control a network; providing a direct current circuitconfigured to carry a loop state direct current; and changing anelectrical characteristic of the direct current circuit so that theelectrical characteristic of the communication apparatus conforms with acommunication standard adopted by another communication apparatus.
 21. Amethod of communicating by interfacing with a telephone line, comprisingthe steps of: providing a network control unit configured to control anetwork; providing a direct current circuit configured to carry a loopstate direct current; and alternating one of the plurality of electricalcharacteristics with another corresponding to a kind of communication.22. Communication means for communicating with another communicatingmeans, the means for communicating including network control means forinterfacing with a telephone line, said network control meanscomprising: means for carrying a loop state direct current; and meansfor changing an electrical characteristic of the loop state directcurrent so that the electrical characteristic of the loop state directcurrent conforms to a communication standard adopted by the anothercommunication means.